Led for plant illumination

ABSTRACT

An epitaxial wafer for plant lighting light-emitting diodes (LED), the epitaxial wafer includes: a growth substrate; a first red-light epitaxial laminated layer; a distributed Bragg reflector (DBR) semiconductor laminated layer; and a second red-light epitaxial laminated layer; wherein: the first red-light epitaxial laminated layer comprises a first N-type ohmic contact layer, a first N-type covering layer, a first light-emitting layer, a first P-type covering layer, and a first P-type ohmic contact layer; and the second red-light epitaxial laminated layer comprises a second N-type ohmic contact layer, a second N-type covering layer, a second light-emitting layer, a second P-type covering layer, and a second P-type ohmic contact layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of, and claims priority to,U.S. patent application Ser. No. 15/594,617 filed on May 14, 2017, whichclaims priority to Chinese Patent Application No. 201610757136.6 filedon Aug. 30, 2016, and is a continuation-in-part of and claims priorityto U.S. patent application Ser. No. 14/415,037 filed on Jan. 15, 2015,which in turn is a national stage application of, and claims priorityto, PCT/CN2013/075684 filed on May 16, 2013, which claims priority toChinese Patent Application No. 201310072627.3 filed on Mar. 7, 2013. Thedisclosures of these applications are hereby incorporated by referencein their entirety.

BACKGROUND

In recent years, many studies have been made on plant cultivation viaartificial light source. In particular, the plant cultivation by thelight-emitting diode (LED) attracts much attention due to excellentmonochromaticity, energy saving, long service life and small size.

Plant illumination mainly includes the plant growth light and aquariumlight. The plant growth light supplements the light source when thenatural light is insufficient, which complements the sunlight andadjusts the agricultural product growth. The aquarium light not onlyimproves the growth of aquatic plants, but also has the lighting effectfor sightseeing.

Compared with traditional plant illumination, the LED plant illuminationis advantageous in the following aspects: i) energy saving. The LEDplant illumination may directly generate the light for plant withsame-lumen photon, which consumes little power; ii) high efficiency. Asmonochromatic light, the LED can generate light waves matching the plantrequirement, which cannot be achieved by traditional plant light; iii)the LED plant illumination has rich wavelength types capable ofcontrolling the plant flowering, fruiting, plant height and nutrientcontents. With the further improvement of LED plant illuminationtechnology, it will be used for multi-layer 3D combined cultivationsystems with less system heat, small space and low thermal load.

SUMMARY

The present disclosure describes an LED for plant illumination,including a new light-emitting material GaxIn_((1-X))As_(Y)P_((1-Y)) ofwhich can significantly improve the light-emitting efficiency by50%-100%.

An LED for plant illumination, comprising a substrate arranged at the PNjunction light-emitting part of the substrate. The light-emitting parthas a strained light-emitting layer with component formula ofGa_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and 0<Y<1).

In some embodiments, the light-emitting part has a strainedlight-emitting layer with component formula ofGa_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and 0<Y<0.2).

In some embodiments, the light-emitting part has a strainedlight-emitting layer with component formula ofGa_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and 0<Y<0.1).

In some embodiments, the light-emitting part has a strainedlight-emitting layer with component formula ofGa_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and 0<Y<0.05).

In some embodiments, the light-emitting part has a barrier layer,forming a 2˜40-pair alternating-layer structure with the strainedlight-emitting layer.

In some embodiments, each alternating-layer structure is 5-100 nm thick.

In some embodiments, the barrier layer has a component formula of(Al_(A)Ga_(1-A))_(B)In_((1-B))P (0.3≤A≤1 and 0<B<1).

In some embodiments, the substrate material may be GaAs, GaP or any oneof their combinations.

In some embodiments, the invention also comprises a buffer layer betweenthe substrate and the light-emitting part.

In some embodiments, the invention also comprises a window layerarranged on the light-emitting part.

In some embodiments, the window layer material is GaP.

In some embodiments, the window layer is 0.5-15 μm thick.

In some embodiments, in the LED for improving photosynthesis duringplant cultivation, the peak light-emitting wavelength of the strainedlight-emitting layer is 650 nm-750 nm.

In some embodiments, in the LED for improving photosynthesis duringplant cultivation, the peak light-emitting wavelength of the strainedlight-emitting layer is 700 nm-750 nm.

In another aspect, an LED is provided for plant illumination, includinga light-emitting part of strained light-emitting layer on the substratewith component formula of Ga_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and0<Y<1). The strained light-emitting layer material is GaInAsP, which canimprove the light-emitting efficiency of the strained light-emittinglayer. In addition, the material is helpful for improving life stabilitydue to the lack of Al component.

In addition, by adjusting the composition and thickness of the strainedlight-emitting layer, the light-emitting wavelength from the strainedlight-emitting layer is in a range of 650 nm-750 nm. In someembodiments, a window layer is provided at the light-emitting part ofthe LED for plant illumination, which is transparent to thelight-emitting wavelength, and therefore will not absorb the light fromthe light-emitting part. In addition, it can have a current spreadingfunction.

Hence, according to some embodiments of this disclosure, a high outputpower and/or highly efficient LED capable of generating a large quantityof light-emitting wavelength of 650 nm-750 nm is provided.

In another aspect, an epitaxial wafer for a plant lighting LED isprovided, including from up to bottom: a growth substrate, a firstred-light epitaxial laminated layer, a distributed Bragg reflector (DBR)semiconductor laminated layer and a second red-light epitaxial laminatedlayer, wherein, the first red-light epitaxial laminated layer comprisesa first N-type ohmic contact layer, a first N-type covering layer, afirst light-emitting layer, a first P-type covering layer and a firstP-type ohmic contact layer; and the second red-light epitaxial laminatedlayer comprises a second N-type ohmic contact layer, a second N-typecovering layer, a second light-emitting layer, a second P-type coveringlayer and a second P-type ohmic contact layer.

In some embodiments, a doping concentration of the DBR semiconductorlaminated layer is ≤5×10¹⁷, to form a high resistance interface.

In some embodiments, light emitting wavelength of the firstlight-emitting layer is 710 nm˜750 nm, and that of the secondlight-emitting layer is 640 nm˜680 nm.

In some embodiments, light emitting wavelength of the firstlight-emitting layer is 730 nm, and that of the second light-emittinglayer is 660 nm.

In some embodiments, an etching stop layer is provided between the DBRsemiconductor laminated layer and the second red-light epitaxiallaminated layer.

In another aspect, an LED chip for a plant lighting LED is provided,including from up to bottom: a first red-light epitaxial laminatedlayer, a DBR semiconductor laminated layer, a second red-light epitaxiallaminated layer and a conductive bonding substrate; in which, the firstred-light epitaxial laminated layer comprises a first N-type ohmiccontact layer, a first N-type covering layer, a first light-emittinglayer, a first P-type covering layer and a first P-type ohmic contactlayer; and the second red-light epitaxial laminated layer comprises asecond N-type ohmic contact layer, a second N-type covering layer, asecond light-emitting layer, a second P-type covering layer and a secondP-type ohmic contact layer; wherein, light-emitting area of the firstred-light epitaxial laminated layer is less than that of the secondred-light epitaxial laminated layer; the first N-type ohmic contactlayer is provided with a first electrode; between the first P-type ohmiccontact layer and the second N-type ohmic contact layer is provided withan electronic-connected structure, and the second P-type ohmic contactlayer is provided with a second electrode.

In some embodiments, light emitting wavelength of the firstlight-emitting layer is 710 nm˜750 nm, and that of the secondlight-emitting layer is 640˜680 nm.

In some embodiments, doping concentration of the DBR semiconductorlaminated layer is ≤5×10¹⁷, to form a high resistance interface.

In some embodiments, surface of the second red-light epitaxial laminatedlayer is preset with a light-emitting zone and a non-light-emittingzone, and a DBR semiconductor laminated layer is formed on thenon-light-emitting zone of the second red-light epitaxial laminatedlayer.

In some embodiments, area of the DBR semiconductor laminated layer isless than the light-emitting area of the second red-light epitaxiallaminated layer, but larger than that of the first red-light epitaxiallaminated layer.

In some embodiments, the non-light-emitting zone on the surface of thesecond N-type ohmic contact layer is provided with an electric diffusionstructure.

In some embodiments, an etching stop layer is provided between the DBRsemiconductor laminated layer and the second red-light epitaxiallaminated layer.

In another aspect, a light-emitting system is provided for plantlighting. The system can include a plurality of the LED chips describedabove. The LED chips can form an array over a packaging frame.

In another aspect, a fabrication method for growing a plant lighting LEDchip is provided, including: 1) epitaxial growth: provide a growthsubstrate, and form any of aforesaid LED epitaxial wafer for plantlighting; 2) substrate transfer: bond a conductive bonding substrate onthe epitaxial wafer surface and remove the growth substrate to exposethe first N-type ohmic contact layer surface of the epitaxial wafer; 3)defining of light-emitting zone: define a first light-emitting zone anda second light-emitting zone on the epitaxial wafer surface, and removethe first N-type ohmic contact layer, the first N-type covering layer,the first light-emitting layer and the first P-type covering layer ofthe second light-emitting zone to expose the first P-type ohmic contactlayer; 4) electrode fabrication: remove the DBR semiconductor laminatedlayer of the second light-emitting zone and expose the surface of thesecond N-type ohmic contact layer; fabricate an N-type electrode on thesurface of the first N-type ohmic contact layer, and fabricate anelectronic-connected structure; electrically connect the first P-typeohmic contact layer and the second N-type ohmic contact layer.

In some embodiments, in step 3), the epitaxial wafer surface is alsodefined with an isolation zone between the first light-emitting zone andthe second light-emitting zone.

In some embodiments, in step 3), remove the second light-emitting zoneand the first N-type ohmic contact layer, the first N-type coveringlayer, the first light-emitting layer and the first P-type coveringlayer of the isolation zone.

In some embodiments, after step 4), the DBR layer is larger than thefirst light-emitting zone but smaller than the second light-emittingzone.

Other features and advantages of the present disclosure will bedescribed in detail in the following specification, and moreover, willbecome obvious partially through the Specification or understood throughimplementations of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and constitute a part of thisspecification, together with the embodiments, are therefore to beconsidered in all respects as illustrative and not restrictive. Inaddition, the drawings are merely illustrative, which are not drawn toscale.

FIG. 1 is a sectional structure diagram of an LED for plant illuminationaccording to some embodiments.

FIG. 2 is a side sectional view of a LED chip for plant lighting inaccordance with Embodiment 7.

FIG. 3 is a top view of the LED chip as shown in FIG. 2.

FIG. 4 illustrates a first step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 5 illustrates a second step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 6 illustrates a third step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 7 illustrates a fourth step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 8 illustrates a fifth step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 9 illustrates a sixth step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 10 illustrates a seventh step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 11 illustrates an eight step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 12 illustrates a ninth step of fabricating an LED chip for plantlighting according to some embodiments.

FIG. 13 illustrates a tenth step of fabricating an LED chip for plantlighting according to some embodiments.

In the drawings:

200: growth substrate; 210: far red-light epitaxial laminated layer;211: first N-type etching stop layer; 212: first N-type ohmic contactlayer; 213: first N-type electrode diffusion layer; 214: first N-typecovering layer; 215: first light-emitting layer; 216: first P-typecovering layer; 217: first P-type ohmic contact layer; 220: DBRsemiconductor laminated layer; 230: super red-light epitaxial laminatedlayer; 231: second N-type etching stop layer; 232: second N-type ohmiccontact layer, 233: second N-type electrode diffusion layer; 234: secondN-type covering layer; 235: second light-emitting layer; 236: secondP-type covering layer; 237: P-type transition layer; 238: second P-typeohmic contact layer; 240: mirror structure; 250: conductive bondinglayer; 260: conductive bonding substrate; 271: N-type electrode; 272:BeAu metal layer; 273: electronic-connected structure; 274: electrodeextension bar; 275: P-type electrode.

DETAILED DESCRIPTION

Based on study results so far, the light-emitting wavelength of lightsources suitable for plant growth is near 450 nm (blue light) and600-750 nm (red light).

The traditional light-emitting layer for plant illumination is AlGaAsPor AlGaAs. However, the LED with light-emitting layer made of AlGaAsP orAlGaAs has low light-emitting output power. To promote feasible lightsource of LED for plant cultivation, it is necessary to develop LED withhigh output power and/or high efficiency in consideration of energy andcost saving.

The following embodiments provide a LED with 650-750 nm wavelengthsuitable for plant illumination, featured by high output power andstable service life.

The GaInP light-emitting wavelength is near 640 nm and the GaAslight-emitting wavelength is near 850 nm. In the following embodiments,the light-emitting layer GaInP material is doped with As and thethickness and strain capacity of the strained light-emitting layer areadjusted; therefore, an LED composed of new epitaxial structure forplant illumination is developed that is suitable for wavelength of650-750 nm.

Detailed descriptions will be given below about this disclosure withreference to accompanying drawings and embodiments.

Embodiment 1

As shown in FIG. 1, an LED comprises: a substrate 11, divided into afirst surface and a second surface; a light-emitting part, whichconsists of a stack of semiconductor material layers, including a bufferlayer 12, a first restriction layer 13, a light-emitting layer 14 and asecond restriction layer 15, sequentially from down up and formed on thefirst surface of the substrate 11; a window layer 16 formed on a partialregion of the second restriction layer 15 of the light-emitting part; asecond electrode 17, formed on the window layer 16; and a secondelectrode 18, formed on the second surface of the substrate 11.

In the element, the substrate 11 material may be GaAs, GaP or any one oftheir combinations.

The buffer layer 12 can mitigate lattice imperfection of the epitaxiallygrowing substrate but is not a necessary film for the element.

The light-emitting part consists of an alternating layer (of strainedlight-emitting layer and barrier layer) structure, including at leasttwo 2 pairs (preferably 2-40 pairs). The structure of each pair ofalternating-layers is, without limitation to, 5-100 nm thick. Astructure of a plurality of alternating layers can effectively improvethe saturation current of the element. In this embodiment, the pairnumber of the alternating layer structure of alternating strainedlight-emitting layer and barrier layer is 6. The structure of each pairis 40 nm thick and the total thickness is 240 nm.

The strained light-emitting layer material is Al-free GaInAsP withcomponent formula of Ga_(X)In_((1-X))As_(Y)P_((1-Y)) (0<X<1 and 0<Y<1).In some embodiments, to better control the peak wave of thelight-emitting layer within 650 nm-750 nm, the Y value is preferably0<Y<0.2. In this embodiment, X=0.5 and Y=0.01.

The barrier layer material is AlGaInP with component formula of(Al_(A)Ga_(1-A))_(B)In_((1-B))P (0.3<A<1 and 0<B<1). In this embodiment,A=0.5 and B=0.5.

The window layer is GaP (thickness: 0.5 μm-15 μm) and is capable ofcurrent expansion. The window layer is not a necessary film for theelement, which can be chosen based on the process parameters.

Referring to Table 1 for the optical-electrical characteristics of the42×42 mil large-power quaternary LED element structure. As shown inTable 1, based on the flowing current results of the first electrode andsecond electrode after being powered on, the element emits red lightwith an average peak wavelength of 685.6 nm. When the 350 mA currentflows through in forward direction, the average forward voltage value is2.25 V and the output power is 250.3 mW.

TABLE 1 VF/V Po/mW WLD/nm WLP/nm No. 1 2.26 248.5 656.2 686.0 No. 2 2.23252.1 656.2 685.1 Average 2.25 250.3 656.2 685.6

Embodiment 2

In comparison with Embodiment 1, t the following is the same: in the42×42 mil quaternary LED element structure of this embodiment, the pairnumber of the alternating-layer (of strained light-emitting layer andbarrier layer) structure is 6. The structure of each pair is 60 nm thickand the total thickness is 360 nm. The difference is that: the strainedlight-emitting layer is Ga_(X)In_((1-X))As_(Y)P_((1-Y)) (X=0.5 andY=0.025). Based on the flowing current results of the first electrodeand second electrode after being powered on, the element emits red lightwith average main wavelength of 680.2 nm and average peak wavelength of714.9 nm. When the 350 mA current flows through in forward direction,the average forward voltage value is 2.22 V and the output power is232.7 mW.

Embodiment 3

In comparison with Embodiment 1, the difference is that: the strainedlight-emitting layer of the 42×42 mil quaternary LED element structureof this embodiment is Ga_(X)In_((1-X))As_(Y)P_((1-Y)) (X=0.5 andY=0.04).

Refer to Table 2 for the optical-electrical characteristics of the 42×42mil quaternary LED element structure. As shown in Table 2, based on theflowing current results of the first electrode and second electrodeafter being powered on, the element emits red light with average peakwavelength of 722.0 nm. When the 350 mA current flows through in forwarddirection, the average forward voltage value is 2.18 V and the outputpower is 216.5 mW.

TABLE 2 VF/V Po/mW WLD/nm WLP/nm No. 1 2.19 215.7 693.7 721.7 No. 2 2.20222.7 697.4 723.5 No. 3 2.16 220.1 701.7 723.5 No. 4 2.19 207.6 691.5719.3 Average 2.19 216.5 696.1 722.0.

Embodiment 4

In comparison with Embodiment 3, the difference is that: the strainedlight-emitting layer of the 42×42 mil quaternary LED element structureof this embodiment is Ga_(X)In_((1-X))As_(Y)P_((1-Y)) (X=0.5 andY=0.05). Based on the flowing current results of the first electrode andsecond electrode after powering on, the element emits red light withaverage main wavelength of 712.3 nm and average peak wavelength of 739.5nm. When the 350 mA current flows through in forward direction, theaverage forward voltage value is 2.21 V and the output power is 202.2mW.

Embodiment 5

In comparison with Embodiment 3, the difference is that: in the 42×42mil quaternary LED element structure of this embodiment, the pair numberof alternating-layer (of strained light-emitting layer and barrierlayer) structure is 9. The structure of each pair is 50 nm thick and thetotal thickness is 450 nm. Based on the flowing current results of thefirst electrode and second electrode after powering on, the elementemits red light with average main wavelength of 701.5 nm and averagepeak wavelength of 733.5 nm. The saturation current is above 2,000 mA.When the 350 mA current flows through in forward direction, the averageforward voltage value is 2.24 V and the output power is 223.9 mW.

To sum up, in the LED element structure for improving photosynthesisduring plant cultivation, the peak light-emitting wavelength can becontrolled within 650-750 nm by adjusting the composition of strainedlight-emitting layer, component value range and the pair number andthickness range of the alternating-layer (of strained light-emittinglayer and barrier layer) structure, thereby achieving high output power.In addition, the material is helpful for improving life stability due tothe lack of Al component.

Embodiment 6

The larger is Y value in the strain light-emitting layerGa_(X)In_((1-X))As_(Y)P_((1-Y)), the narrower is the material gap, andthe longer is the light emitting wavelength. Moreover, mismatch degreebetween the light emitting portion and base gets larger, and latticegrowth quality of material gets poorer. As evidenced by experiment, as Ychanges from 0 to 0.1, mismatch degree of the light emitting portionmaterial increases gradually and lattice growth quality gets poorer. Asthe comparison examples No. 1˜No. 8 in Table 3 shown, when b value ofthe barrier layer (Al_(A)Ga_(1-A))_(B)In_((1-B))P and total thickness ofthe alternating laminated structure in light emitting portion (MQWstructure) remain unchanged, if Y is 0.01, light emitting efficiency ishighest.

With As added in the light emitting layer, lattice constant of thestrain light-emitting layer in the light-emitting zone is larger thanthat of GaAs, thus generating compression strain. Therefore, to reducesuch compression strain, a barrier layer (Al_(A)Ga_(1-A))_(B)In_((1-B))Pis designed, wherein, 0.5<B≤0.52, i.e., lattice constant of the barrierlayer is less than that of the GaAs base, thus generating tensionstrain. With a combination of the light-emitting zone and the barrierlayer, effect and substrate mismatch degree get smaller to improvelight-emitting efficiency and reliability of the material. As shown inTable 3, when B is 0.52, the light-emitting efficiency is highest.

For a MQW structure, total tension strain=compression strain of strainlight-emitting layer (quantum well)*well thickness (positive)+tensionstrain of barrier layer (quantum barrier)*barrier thickness (negative).Total tension strain is preferred to be less than 500 ppm and preferably100˜200 ppm as evidenced by an experiment. To achieve high-lightingefficiency LED with 650˜750 nm light-emitting wavelength, as shown inoptimized experiment results, when B=0.52 in the barrier layer(Al_(A)Ga_(1-A))_(B)In_((1-B))P and Y=0.01 in the light-emitting layerGa_(X)In_((1-X))As_(X)P_((1-Y)), and total thickness is 360 nm,light-emitting effect of LED is best, reaching 1.5-2 times compared withconventional method.

TABLE 3 No. 1 2 3 4 5 6 7 8 Y value 0 0.01 0.025 0.01 0.01 0.01 0.010.01 [Light emitting layer Ga_(x)In_((1-x))AS_(y)P_((1-y))] b value 0.50.5 0.5 0.5 0.52 0.53 0.52 0.52 [Barrier layer(Al_(A)Ga_(1-A))_(B)In_((1-B))P] Total thickness 240 240 240 240 240 240360 450 of MQW/nm (Po/VF/350 mA) 13.70% 28.80% 27.90% 28.40% 29.10%28.30% 30.50% 27% Light-emitting efficiency (Po/VF/350 mA)

Embodiment 7

It is common to pack the deep-blue-light, ultra-red-light andfar-red-light LED chip with single wavelength one by one, and assembleindividual packages on the light plate in various arrangements, as shownin FIG. 14. Due to limited space and cost, it is better to use less LEDsin smaller size.

This embodiment discloses a LED for plant lighting, in which, ultra-redlight (˜660 nm) and far-red light (˜730 nm) for plant lighting arerealized in a single chip via laminated layer epitaxy.

With reference to FIG. 2, a vertical LED chip according to the presentinvention is provided, comprising: a far-red-light epitaxial laminatedlayer 210, a distributed Bragg reflector (DBR) semiconductor laminatedlayer 220, a ultra-red-light epitaxial laminated layer 230, a mirrorstructure 240, a conductive bonding layer 250, a conductive substrate260, an N-type electrode 271 and a P-type electrode 275,

Wherein, light-emitting wavelength of the far-red-light epitaxiallaminated layer 210 is 710 nm˜750 nm, preferably, ˜730 nm, and that ofthe far-red-light epitaxial laminated layer 210 is 640 nm˜680 nm,preferably, ˜660 nm. In some embodiments, lighting area 210 a of thefar-red-light epitaxial laminated layer 210 is less than or equals tolighting area 230 a of the ultra-red-light epitaxial laminated layer230. Preferably, lighting area 210 a of the far-red-light epitaxiallaminated layer 210 is one-third of lighting area 230 a of theultra-red-light epitaxial laminated layer 230.

The DBR semiconductor laminated layer 220 is located between thefar-red-light epitaxial laminated layer 210 and the ultra-red-lightepitaxial laminated layer 230. On the one hand, it reflects far redlight emitted by the far-red-light epitaxial laminated layer 210 andprevents such light from being absorbed by the ultra-red-light epitaxiallaminated layer 230; on the other hand, a high-resistance interface isformed as a current blocking layer to make current flow to thelight-emitting zone of the ultra-red-light epitaxial laminated layer230, which has no far-red-light epitaxial laminated layer 210, so as toimprove luminance. Therefore, doping concentration of the DBRsemiconductor laminated layer 220 is preferred to be not more than5×10¹⁷, and preferably 4.00×10¹⁷.

The far-red-light epitaxial laminated layer 210 and the ultra-red-lightepitaxial laminated layer 230 can be made of AlGaInP-based material,wherein, the far-red-light epitaxial laminated layer 210, from up tobottom, comprises an N-type ohmic contact layer 212, a first N-typeelectrode diffusion layer 213, a first N-type covering layer 214, afirst light emitting layer 215, a first P-type covering layer 216 and afirst P-type ohmic contact layer 217; and the ultra-red-light epitaxiallaminated layer 230, from up to bottom. comprises a second N-type ohmiccontact layer 232, a second N-type electrode diffusion layer 233, asecond N-type covering layer 234, a second light emitting layer 235, asecond P-type covering layer 236, a P-type transition layer 237 and asecond P-type ohmic contact layer 238. An N-type etching stop layer 231can be provided between the ultra-red-light epitaxial laminated layer230 and the DBR semiconductor laminated layer 220.

A step-shaped structure is provided between the far-red-light epitaxiallaminated layer 210 and the ultra-red-light epitaxial laminated layer230 for fabricating an electronic-connected structure 271, wherein, oneend is connected to the ohmic contact layer 261 of the far-red-lightepitaxial laminated layer 210, and the other end is connected to theohmic contact layer 237 of the ultra-red-light epitaxial laminated layer230. Preferably, as lighting area 230 a of the ultra-red-light epitaxiallaminated layer 230 is larger than lighting area 210 a of thefar-red-light epitaxial laminated layer 210, an extension bar 274 can beset on the ohmic contact layer 237 of the ultra-red-light epitaxiallaminated layer 230 to ensure even light-emitting of the light emittinglayer, as shown in FIG. 3.

With reference to FIGS. 4-13 and fabrication method, the structure ofthe LED chip is described in detail below, mainly comprising: (I)epitaxial growth; (II) substrate transfer; (III) defining oflight-emitting zone; (IV) electrode fabrication.

(I) Epitaxial Growth

Form an epitaxial structure on the growth substrate, as shown in FIG. 4.The key of the structure is to grow an epitaxial layer as shown in Table4 on the GaAs substrate in sequence. It should be noted that only onetypical material is listed in the table below for material of each layerof the epitaxial structure. The material in actual application is notlimited to the listed one but can be expended to any other necessarymaterials.

TABLE 4 Thickness Doping Function Layer Material (nm) concentrationP-type ohmic P-GaP GaP:Mg ≥500 ≥8.00 × 10¹⁷ contact layer (2) P-typetransition P-AlGaInP AlGaInP:Mg ≤100 ≥2.00 × 10¹⁸ layer P-type coveringP-AlInP (2) AlInP:Mg ≥500 ≥1.20 × 10¹⁸ layer (2) ~660 nm lightGaInP-well GaInP ≥8 × 3 — emitting layer AlGaInP-barrier AlGaInP ≥8 × 3— N-type covering N-AlInP (2) AlInP:Si ≥500 ≥1.60 × 10¹⁸ layer (2)N-type current N-AlGaInP (2) AlGaInP:Si ≥1000  ≥1.00 × 10¹⁷ diffusionlayer (2) N-type ohmic N-GaAs (2) GaAs:Si ≥100 ≥6.00 × 10¹⁸ contactlayer (2) N-type etching stop N-GaInP (2) GaInP:Si ≥100 ≥1.00 × 10¹⁸layer (2) DBR semiconductor P-AlAs AlAs:Mg ≥54.5 × 2   ≤5.00 × 10¹⁷laminated layer P-AlGaAs AlGaAs:Mg ≥50.9 nm × 2 ≤5.00 × 10¹⁷ P-typeohmic P-GaAs GaAs:Mg ≥500 ≥1.00 × 10¹⁸ contact layer (1) P-type coveringP-AlInP (1) AlInP:Mg ≥900 ≥1.20 × 10¹⁸ layer (1) ~730 nm lightAlGaAs-well AlGaAs ≥12 × 3  — emitting layer (1) AlGaInP-barrier AlGaInP≥13 × 3  — N-type covering N-AlInP (1) AlInP:Si ≥500 ≥1.60 × 10¹⁸ layer(1) N-type current N-AlGaInP (1) AlGaInP:Si ≥1000  ≥1.00 × 10¹⁷diffusion layer (1) N-type ohmic N-GaAs (1) GaAs:Si ≥100 ≥6.00 × 10¹⁸contact layer (1) N-type etching stop N-GaInP (1) GaInP:Si ≥100 ≥1.00 ×10¹⁸ layer (1) GaAs substrate

(II) Substrate Transfer

In this step, bond the conductive substrate 260 and remove the growthsubstrate. To reach sufficient light emitting efficiency, a mirrorstructure is designed between the conductive substrate 260 and theepitaxial structure. In the embodiments below, at first, fabricate amirror structure before substrate transfer. Details are as follows.

At first, on the surface of the second P-type ohmic contact layer 238 ofthe epitaxial structure, plate a light-transmission dielectric layer,and make a hole on the dielectric layer to remove the plated P-typemetal ohmic contact layer (such as AuZn) and metal mirror layer (such asAu) to form a mirror structure 240. According to a variant, deposit atransparent conducing layer (such as ITO) and a metal mirror layer (suchas Ag) on the surface of the second P-type ohmic contact layer 238 insequence to form another mirror structure.

Next, plate a bonding layer 250 on the mirror structure 240, and performbonding for the conductive substrate 260 with a bonding layer tocomplete metal bonding. The structure is shown in FIG. 5. The metalbonding layer 250 can be made of Au/Au, Au/In, Au/Sn, Ni/Sn.

Remove GaAs substrate with alkaline solution and the first N-typeetching stop layer 211 with hydrochloride acid solution and expose thefirst N-type ohmic contact layer 212 to complete substrate transfer, asshown in FIG. 6.

(III) Defining of Light-Emitting Zone

Preset a far-red-light light-emitting zone 210 a on surface of the firstN-type ohmic contact layer 212 of the epitaxial structure, and removethe first N-type ohmic contact layer 212, the first N-type currentdiffusion layer 213, the first N-type covering layer 214, the firstlight emitting layer 215, the first P-type covering layer 216 of thefar-red-light light-emitting zone 210 to expose the first P-type ohmiccontact layer 217, as shown in FIG. 7. The far-red-light light-emittingzone 210 a can be referred to FIG. 3.

(IV) Electrode Fabrication

At first, fabricate a BeAu metal layer 272 on surface of the firstP-type ohmic contact layer 217, and form ohmic contact with the firstP-type ohmic contact layer 217 after annealing, as shown in FIG. 8.

Next, preset an ultra-red-light light-emitting zone 230 a on surface ofthe first P-type ohmic contact layer 217 and remove the first P-typeohmic contact layer 217, the DBR semiconductor laminated layer 220 andthe second N-type etching stop layer 231 of ultra-red-lightlight-emitting zone 230 a to expose the second N-type ohmic contactlayer 232, as shown in FIG. 9. Remove the first P-type ohmic contactlayer 217 and the DBR semiconductor laminated layer 220 with phosphoricacid solution, and remove the second N-type etching stop layer 231 withhydrochloride acid solution.

Remove the second N-type ohmic contact layer 232 with LIT Litho orphosphoric acid solution and leave the ohmic contact zone forpatterning, as shown in FIG. 10. The remaining portion can be referredto corresponding areas of the electronic-connected structure 273 and theelectrode extension bar 274 as shown in FIG. 3.

Next, evaporate GeAu on the first N-type ohmic contact layer 212 as theN-type electrode 271, and form GeAu metal on the second N-type ohmiccontact layer 232, and connect it to the BeAu metal layer 272 on surfaceof the first P-type ohmic contact layer 217 as an electronic-connectedstructure 273 and an electrode extension bar 274. Form ohmic contactafter annealing, as shown in FIG. 11.

Next, singularize the chip and remove part of the second N-typeelectrode diffusion layer 233, the second N-type covering layer 234, thesecond light emitting layer 235, the second P-type covering layer 236and the P-type transition layer 237, till the second P-type ohmiccontact layer 238 for patterning, as shown in FIG. 12.

In some embodiments, form a light-intensifying structure on surfaces ofthe first N-type electrode diffusion layer 213 and the second N-typeelectrode diffusion layer 233 with hydrochloride acid solution, as shownin FIG. 13.

Last, form a P-type electrode 275 on back of the conductive substrate260 to complete a vertical LED chip for plant lighting.

With a combination of epitaxial growth of ultra-red-light andfar-red-light laminated layer and chip fabrication, this embodimentreduces number of packages and area of plant lighting plate, andtherefore cut cost.

All references referred to in the present disclosure are incorporated byreference in their entirety. Although specific embodiments have beendescribed above in detail, the description is merely for purposes ofillustration. It should be appreciated, therefore, that many aspectsdescribed above are not intended as required or essential elementsunless explicitly stated otherwise. Various modifications of, andequivalent acts corresponding to, the disclosed aspects of the exemplaryembodiments, in addition to those described above, can be made by aperson of ordinary skill in the art, having the benefit of the presentdisclosure, without departing from the spirit and scope of thedisclosure defined in the following claims, the scope of which is to beaccorded the broadest interpretation so as to encompass suchmodifications and equivalent structures.

1. An epitaxial wafer for plant lighting light-emitting diodes (LED),the epitaxial wafer comprising: a growth substrate; a first red-lightepitaxial laminated layer; a distributed Bragg reflector (DBR)semiconductor laminated layer; and a second red-light epitaxiallaminated layer; wherein: the first red-light epitaxial laminated layercomprises a first N-type ohmic contact layer, a first N-type coveringlayer, a first light-emitting layer, a first P-type covering layer, anda first P-type ohmic contact layer; and the second red-light epitaxiallaminated layer comprises a second N-type ohmic contact layer, a secondN-type covering layer, a second light-emitting layer, a second P-typecovering layer, and a second P-type ohmic contact layer.
 2. Theepitaxial wafer of claim 1, wherein a doping concentration of the DBRsemiconductor laminated layer is ≤5×10¹⁷ to thereby form ahigh-resistance interface.
 3. The epitaxial wafer of claim 1, wherein alight emitting wavelength of the first light-emitting layer is 710nm-750 nm, and a light emitting wavelength of the second light-emittinglayer is 640 nm-680 nm.
 4. The epitaxial wafer of claim 3, wherein thelight emitting wavelength of the first light-emitting layer is 730 nm,and the light emitting wavelength of the second light-emitting layer is660 nm.
 5. The epitaxial wafer of claim 1, further comprising an etchingstop layer disposed between the DBR semiconductor laminated layer andthe second red-light epitaxial laminated layer.
 6. A light-emittingdiode (LED) chip for plant lighting, comprising: a first red-lightepitaxial laminated layer; a distributed Bragg reflector (DBR)semiconductor laminated layer; a second red-light epitaxial laminatedlayer; and a conductive bonding substrate; wherein: the first red-lightepitaxial laminated layer comprises a first N-type ohmic contact layer,a first N-type covering layer, a first light-emitting layer, a firstP-type covering layer, and a first P-type ohmic contact layer; and thesecond red-light epitaxial laminated layer comprises a second N-typeohmic contact layer, a second N-type covering layer, a secondlight-emitting layer, a second P-type covering layer, and a secondP-type ohmic contact layer; a light-emitting area of the first red-lightepitaxial laminated layer is less than a light-emitting area of thesecond red-light epitaxial laminated layer; the first N-type ohmiccontact layer is provided with a first electrode; between the firstP-type ohmic contact layer and the second N-type ohmic contact layer isprovided with an electrical coupling structure; and the second P-typeohmic contact layer is provided with a second electrode.
 7. The LED chipof claim 6, wherein a doping concentration of the DBR semiconductorlaminated layer is ≤5×10¹⁷ to thereby form a high-resistance interface.8. The LED chip of claim 6, wherein a light emitting wavelength of thefirst light-emitting layer is 710 nm-750 nm, and a light emittingwavelength of the second light-emitting layer is 640 nm-680 nm.
 9. TheLED chip of claim 8, wherein the light emitting wavelength of the firstlight-emitting layer is 730 nm, and the light emitting wavelength of thesecond light-emitting layer is 660 nm.
 10. The LED chip of claim 6,further comprising an etching stop layer between the DBR semiconductorlaminated layer and the second red-light epitaxial laminated layer. 11.The LED chip of claim 6, wherein: a surface of the second red-lightepitaxial laminated layer is preset with a light-emitting area and anon-light-emitting area; and the DBR semiconductor laminated layer isformed on the non-light-emitting zone of the second red-light epitaxiallaminated layer.
 12. The LED chip of claim 11, wherein the DBRsemiconductor laminated layer is smaller than the light-emitting area ofthe second red-light epitaxial laminated layer, but larger than alight-emitting area of the first red-light epitaxial laminated layer.13. The LED chip of claim 11, further comprising an electrical currentdiffusion structure disposed over a non-light-emitting area of thesecond N-type ohmic contact layer.
 14. A fabrication method of a plantlighting light-emitting diode (LED) chip, the method comprising: (1)epitaxial growth: provide a growth substrate, and form any of aforesaidLED epitaxial wafer for plant lighting; (2) substrate transfer: bond aconductive bonding substrate on the epitaxial wafer surface and removethe growth substrate to expose the first N-type ohmic contact layersurface of the epitaxial wafer; (3) defining of light-emitting zone:define a first light-emitting zone and a second light-emitting zone onthe epitaxial wafer surface, and remove the first N-type ohmic contactlayer, the first N-type covering layer, the first light-emitting layerand the first P-type covering layer of the second light-emitting zone toexpose the first P-type ohmic contact layer; (4) electrode fabrication:remove a distributed Bragg reflector (DBR) semiconductor laminated layerof the second light-emitting zone and expose the surface of the secondN-type ohmic contact layer; fabricate an N-type electrode on the surfaceof the first N-type ohmic contact layer, and fabricate anelectronic-connected structure; electrically connect the first P-typeohmic contact layer and the second N-type ohmic contact layer.
 15. Themethod of claim 14, wherein in step (3), the epitaxial wafer surface isalso defined with an isolation zone between the first light-emittingzone and the second light-emitting zone.
 16. The method of claim 15,wherein in step (3), the method further comprises removing the secondlight-emitting zone and the first N-type ohmic contact layer, the firstN-type covering layer, the first light-emitting layer and the firstP-type covering layer of the isolation zone.
 17. The method of claim 16,wherein after step (4), the DBR layer is larger than the firstlight-emitting zone but smaller than the second light-emitting zone. 18.The method of claim 17, wherein a doping concentration of the DBRsemiconductor laminated layer is ≤5×10¹′ to thereby form ahigh-resistance interface.
 19. The method of claim 18, wherein a lightemitting wavelength of the first light-emitting layer is 730 nm, and alight emitting wavelength of the second light-emitting layer is 660 nm.20. The method of claim 19, further comprising: forming an etching stoplayer between the DBR semiconductor laminated layer and the secondred-light epitaxial laminated layer; and forming an electrical currentdiffusion structure over a non-light-emitting area of the second N-typeohmic contact layer.